A conventional apparatus for marking a pattern on an article with a laser comprises a light source from which a laser beam radiates, a mask pattern on a thin metal plate or glass on which a predetermined mark (such as the name of a manufacturer of products or a number of a lot thereof, like IC plastic mold packages, transistors etc.) is formed; and a lens system by which the laser beam is focussed on the products as mentioned above to mark the pattern thereon in accordance with the energy thereof.
In operation, the light source is driven with by use of a predetermined high frequency power source so that the laser beam radiates therefrom to be passed through the mask pattern. The laser beam which is passed through the mask pattern goes into the lens system thereby converging on the products to be marked so that the name of a manufacturer, number of a lot etc. thereof is marked thereon.
According to the conventional apparatus for marking a pattern on an article with a laser, however, the laser beam radiating from the light source is partly reflected by the non-letters portions of the mask pattern (in other words, portions through which the laser beam is interrupted and prevented from being passed). It is also partly reflected by the surface of the products to be marked etc. Thus, the laser beam is scattered from these surfaces. As a result, up to half the energy of the laser beam, or even more, is not utilized, so that the efficiency of energy is decreased. In addition, the energy of the laser beam that is reflected by the mask pattern is so large that parts to be used therein are damaged.